Control electrode for electron discharge devices



April 3, W34. D H. w. PARKER CONTROL ELECTRODE FOR ELECTRON DISCHARGE DEVICES Filed Nov. 12, 1931 En -ml.

ENVENTOR HEnm W. Pmkm" %j ATTORNEY Patented Apr. 3, 1934 PATENT CFFICE CONTROL ELECTRODE FOR ELECTRON DIS- CHARGE DEVICES Henry W. Parker, Toronto, Ontario, Canada, as-

signor to Rogers Radio Tubes, Limited, Toronto, Ontario, Canada, a corporation of Ontario,

Canada Application November 12, 1931, Serial No. 574,471

6 Claims.

tion consists in providing a control electrode for thermionic tubes by the use of which the shrinkage in the manufacture of such tubes is materially reduced.

I A still further object contemplated by my invention comprises producing a control electrode for thermionic tubes which greatly increases the sensitivity of such tubes.

Control electrodes used in cooperation with heated cathodes which are coated with high electron emissive substances such as barium and strontium oxides, or similar alkaline earth oxides, become coated during the process of manufacture of the tube with a deposit of the high emissive material and, due to the proximity of such control electrodes to the hot cathode, emit electrons. Such emission is known as primary emission.

The primary emission of electrons from control electrodes is a serious defect in thermionic tubes which the manufacturers of such tubes have sought to eliminate in many different ways for some time. A deposit of barium on the structure of the control electrode is most often the cause of primary emission from the control electrode and because of the low work function of the barium such a deposit on the electrode is capable of emitting electrons at very low temperature and as the control electrode is usually located in quite close proximity to the heated cathode, the temperature of the control electrode is usually high enough to facilitate such emission of electrons. Although this emission of electrons from the control electrode is usually of the order of only a few microamperes, it tends to reduce the sensitivity of the tube enormously and is particularly bad in recently manufactured tubes, although it is present during the life of the tube in varying degrees.

Various methods have been used hitherto in an attempt to control such undesired primary emission, such as changing the surface layer of the control electrode to render it inactive for any barium deposits, applying colloidal graphite upon the control electrode in order to cover up the metal of the electrode, modifying the nature of the cathode coating so that the transfer of barium from the cathode is diminished and further attempting to reduce the temperature of the control electrode by the use of heavy side rods or supports for the wires composing the electrode in order to conduct the heat away therefrom and reduce the mean value of the electrode temperature.

I have experimented with and tried all of the above recitedmethods and have found that none of them accomplish in a real degree the reduction of primary electron emission from the control electrode. I accomplish such reduction in substantially a one hundred percent manner by processing the surface of the control electrode wires and supports in a manner hereinafter described to produce differential thermal emission from the control electrode wires and supports and thus lower the temperature thereof to a degree insufiicient to permit primary electron emission therefrom.

In the drawing accompanying and forming a part of this specification and in which like reference numerals designate corresponding parts throughout:

Fig. 1 is a partially broken elevation of the elements of a simple three-electrode thermionic tube showing'the relative position of the electrode therein employed in my invention;

Fig. 2 is a greatly enlarged view of a section of thecontrol electrode in Fig. 1; and

Fig. 3 is a greatly enlarged view of a section of the electrode winding mandrel showing the electrode thereon in a position to be processed.

Referring now to the figures, I have elected for convenience and simplicity to describe my in.- vention as applied to the control electrode of an ordinary three-element thermionic tube. In Fig. 1 I have illustrated the elements of such a thermionic tube, with the enclosing envelope omitted, comprising the usual stem and press 1 for supporting by means of supports 12 and l3 and standards '7 and 6, respectively, the anode 2.

The support 12 and standard 7 serve as a terminal for the anode. The supports 16 and 17 serve to support the cathode 4 and also act as terminals for the usual heater element. A terminal 18 for the cathode is provided. Between serves as a terminal therefor. Spacers 9 and 10 of mica or other insulating refractory material serve to maintain the electrodes in their relative positions.

In carrying out my invention, I provide a surface for the wire 8 and standards 3 and 5 having a differential thermal emissivity either by coating a portion of the control electrode wire and supports with a paint to produce a surface therefor having relatively high thermal emissivity or, preferably, by providing a surface for the elements of the control electrode, which are furthest removed from the cathode, having a roughened texture in order to increase the thermal emissivity thereof.

In carrying out my invention I prefer to form the electrode wire 8 upon a mandrel 11 as shown in Fig. 3 utilizing for the supports 3 and 5 wires of nickel or molybdenum previously highly polished and wind thereon and weld thereto the wire 8 of nickel or molybdenum similarly highly polished. After the wire has been wound to the desired length and before removal from the mandrel, I subject the electrode to a sand blast, as

indicated by the arrows in Fig. 3, to produce upon substantially the entire exposed area of the wire 8 and the standards 3 and 5 a roughened surface.

It is an elementary physical principle that a polished metal surface has a thermal emissivity of approximately one-tenth that of a black body and that a sand-blasted metal surface has a thermal emissivity of approximately thirty percent that of a black body. Thus, the relatively thermal emissivity of a polished body and a sandblasted body is approximately one to three. In other words, my novel control electrode receives heat from the cathode at the rate of one unit and radiates heat away from the electrode at the rate of three units. The equilibrium temperature of the electrode as a whole is therefore very much lower than that of such electrodes in common use inwhich the heat received and radiated is approximately equal My experiments have proven that with an electrode constructed as above described the equilibrium temperature is such as to permit substantially no primary electron emission therefrom and I am able to reduce primary emission practically one hundred percent to eliminate such serious defect.

Obviously, instead of sand-blasting the electrode, substantially fifty percent of the surface area thereof may be covered with a black metallic paint or lamp black, or some other equally effective agent for producing the desired differential thermal emissivity. I prefer, however, as above recited, to employ the process of sandblasting or otherwise roughening the surface to produce the desired effect.

Having thus completely described my invention, what I claim as being new and original and desire to secure by Letters Patent of the United States is as follows:

- a high thermal emissivity.

1. A control electrode for an electron discharge device comprising, a conductor disposed in the form of a helix with that portion of said conductor forming the inner surface of the helix highly polished, and that portion of said conductor forming the outer surface of the helix roughened.

2. An electron discharge device enclosing a cathode and a control electrode adjacent said cathode and comprising a conductor disposed in the form of a helix, the portion of said conductor forming the inner surface of the helix being highly polished to have a low thermal emissivity and the portion of said conductor forming the outer surface of the helix being roughened to have 3. An electron discharge device enclosing a cathode and control electrode completely surrounding said cathode, said control electrode comprising a conductor disposed in the form of a helix, the portion of said conductor forming the inner surface of the helix being highly polished to have a low heat emissivity and the portion of said conductor forming the outer surface of the helix being roughened to have a high thermal emissivity.

4. A control electrode for an electron discharge device comprising, a conductor disposed in the form of a helix with that portion of said conductor forming the inner surface of the helix highly polished, and that portion of said conductor forming the outer surface of the helix roughened, whereby the equilibrium temperature of said control element as a whole is maintained lower than that necessary for the primary emission of electrons therefrom. 110

5. An electron discharge device enclosing a cathode and a control electrode adjacent said cathode and comprising a conductor disposed in the form of a helix, the portion of said conductor forming the inner surface of the helix being 1 highly polished to have a low thermal emissivity and the portion of the conductor forming the outer surface of the helix being roughened to have a high thermal emissivity, whereby said control 7 electrode may as a whole be maintained at a temperature lower than that required for the primary emission of electrons therefrom.

6. An electron discharge device enclosing a cathodeand a control electrode completely surrounding said cathode, said control electrode com- 12 prising a conductor disposed in the form of a helix, the portion of said conductor forming the inner surface of the helix being highly polished to have a low heat emissivity and the portion of said conductor forming the outer surface of the helix being roughened to have a high thermal emissivity whereby the equilibrium temperature of said control electrode as a whole is maintained below a value necessary for the primary emission of electrons therefrom. 3

I HENRY W. PARKER.

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